This invention relates to a novel anti-static, abrasion-resistant optical element, particularly a plastic ophthalmic lens having a conductive layer deposited on at least one surface and an abrasion-resistant coating adhered thereto and to novel and improved methods of making such optical elements.
The term static electricity denotes the group of phenomena associated with the accumulation of electrical charges. Attraction of small particles by an electrically charged body is due to the induced charge. By approaching another insulator (dirt, ash, etc.) the negatively charged body repels the electrons at the surface of the particles. Thus their surface becomes positively charged and attraction results. After contact is established, the charge in the small particle is gradually neutralized; eventually the particle attains a negative charge and is repelled.
The build-up of static charge on plastic elements (especially plastic ophthalmic lenses coated with abrasion-resistant coatings) attracts dust and is unacceptable in many applications (e.g., polycarbonate safety lenses in steel mills, cotton mills and coal mines). In the case of eyewear, these dust particles cause light scattering or haze which can severely limit the visual acuity of the wearer and necessitates frequent cleaning.
Certain topical treatments are commercially available for the prevention of static charge build-up, but these topical treatments are short lived and must be continually repeated.
Another way of preventing the build-up of static charge on plastic lenses is to imbibe anti-static agents into the plastic materials. However, these anti-static agents are known eye irritants and may not be suitable for ophthalmic purposes. Furthermore, these anti-static agents are designed to migrate to the surface where they can interfere with the coating/substrate interface.
Accordingly, it is the principal object of the present invention to prevent the build-up of static charge on optical elements.
It is a further object of the present invention to prevent the build-up of static charge on plastic ophthalmic lenses coated with abrasion-resistant coatings.
It is still a further object of the present invention to produce an anti-static abrasion-resistant optical element that is neither moisture or wear sensitive.